Just for the conversation sake.
we are running,
Your BH (merc or ptech) should have some good aoe for the adds.
Sorc will have good aoe.
If jugg is rage he will have good aoe, but it requires a lot of movement in this case. Jugg and marauder should toss a smash or whatever at the adds though if its convenient.
Also when I tank this on my ptech, I like to drop an explosive dart and DFA on the little guys. Does appreciable damage to groups.
Healers probably won't be able to help out much here as there's a decent amount of damage going out when all the adds are up.
I just really think something else is going on here if the 1800 DPS number is real as you said. Just seems off.